refactor: spin geoipx off geolocate (#893)

A bunch of packages (including oohelperd) just need the ability to
use MaxMind-like databases. They don't need the additional functionality
implemented by the geolocate package. Such a package, in fact, is
mostly (if not only) needed by the engine package.

Therefore, move code to query MaxMind-like databases to a separate
package, and avoid depending on geolocate in all the packages for
which it's sufficient to use geoipx.

Part of https://github.com/ooni/probe/issues/2240

internal/engine/experiment/webconnectivity/control.go

@@ -3,7 +3,7 @@ package webconnectivity
 import (
 	"context"
 
-	"github.com/ooni/probe-cli/v3/internal/engine/geolocate"
+	"github.com/ooni/probe-cli/v3/internal/geoipx"
 	"github.com/ooni/probe-cli/v3/internal/httpx"
 	"github.com/ooni/probe-cli/v3/internal/model"
 	"github.com/ooni/probe-cli/v3/internal/netxlite"
@@ -122,9 +122,7 @@ func Control(
 func (dns *ControlDNSResult) FillASNs(sess model.ExperimentSession) {
 	dns.ASNs = []int64{}
 	for _, ip := range dns.Addrs {
-		// TODO(bassosimone): this would be more efficient if we'd open just
-		// once the database and then reuse it for every address.
-		asn, _, _ := geolocate.LookupASN(ip)
+		asn, _, _ := geoipx.LookupASN(ip)
 		dns.ASNs = append(dns.ASNs, int64(asn))
 	}
 }